Observing spin polarization in single atoms

Understanding the behavior of individual atomic spins in condensed-matter environments is important for the development of spintronics, quantum-information systems, and other novel applications. In a new advance toward that understanding, physicists from the University of California, Berkeley, and the US Naval Research Laboratory have now directly observed the spin polarization of individual magnetic iron and chromium atoms adsorbed on a surface. Such measurements have proved challenging in the past because of the low energy barrier for spin fluctuations. The team overcame that difficulty by sprinkling atoms on islands of ferromagnetic cobalt; the image here shows Fe adatoms as green protrusions on the triangular Co islands. The coupling between the adatoms and the Co kept the adatom spins stationary at the experiment's low temperatures. The researchers probed the spin orientation of adatoms using a scanning tunneling microscope outfitted with a magnetic tip. When the tip was over an adatom, the tunneling...